Friday, November 30, 2012

Eclipse serves servlets on the quick.

You know I always say that it is better to learn something the manual way first before seeing it done the automatic way.  In this post, we created a servlet, but we did it the manual way.  Slowly adding the annotation, extending the class, over riding the methods we needed to over ride.

However, this isn't the 1990's.  Your IDE will do most of your work for you if you like.  When we right moused clicked you may have noticed something that I didn't touch on in the last post.  Here's a photo of what I'm talking about.

Wait, what?!  Add Servlet?!
Yes, that is correct.  Eclipse has a wizard for adding servlets to your project.  So let's go ahead and see what this wizard does by adding a Goodbye servlet.

Here's step 1 of the wizard:

Basic servlet properties
Here on step 1, you pick the class name of the servlet and the package it will be located in.  REMEMBER:  It is strongly recommend to not leave the package name blank, especially for web applications that are going to be facing the public web.  I cannot stress that enough.

Okay so I'm going to create my SayGoodByeServlet in the com.blogger.testing package, since I already have my SayHelloServlet in the same package.  On to step 2!

Basic Annotation properties for servlets
This step covers pretty much the stuff you'd see in the annotations, in this case the @WebServlet annotation.  When it comes to annotations it's pretty much convention over configuration.  If you change nothing here, then your @WebServlet annotation will follow convention.  Everything here is acceptable except the URL mapping.  I would like it to be "/Goodbye" so I'll click on it, click Edit and change that.

That's better
Now that we have that all setup let's move on to step 3!

The meat and potatoes of the class
Ah as you can see from this step, the wizard wants to know which methods you'd like to over ride.  By default the doGet and doPost are already selected.  Pretty much everyone on this planet is pretty convinced that at a minimum, these two should always be overridden.  I would have to agree with that, except in the case of super simple test servlets that people do on web blogs.  Pretty much you can get away with just doGet for "Hello, World!" but beyond that, you're going to at some point need doPost, to do anything useful with servlets.

Everything on this final step is fine as is, so I'll click the finish button., the generated code appears in the code editor windows.  Here's what it says:

package com.blogger.testing;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class SayGoodByeServlet
 */
@WebServlet("/Goodbye")
public class SayGoodByeServlet extends HttpServlet {
 private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public SayGoodByeServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

 /**
  * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
  */
 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  // TODO Auto-generated method stub
 }

 /**
  * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
  */
 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  // TODO Auto-generated method stub
 }

}

As you can see the automatically generated code, is pretty much on par with the code that we wrote just the other day.  Now we can remove those TODO comments and put down some actual code that will tell our system what to do.  Publish the new information to the server and see the wonderful results.

Having a good start on manually building a servlet really helps you to understand the bits that the wizard is doing for you automatically.  So I really recommend getting a peek at how it is done manually and then come and do this and see how it is done automatically.

Cheers!
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